US Reports Unusually Large Increase in Cyclosporiasis Cases

• The US is experiencing an unusually large increase in cyclosporiasis activity, driven by a major multistate outbreak and elevated seasonal transmission across multiple states.  

• Additional cases are highly likely through August as seasonal transmission continues, surveillance data are updated, and investigations continue.

• Federal investigators have identified shredded iceberg lettuce served at multiple locations of a national fast-food restaurant chain in five states as the likely source of the multistate outbreak.

• Although investigators have identified the likely outbreak vehicle, determining the full extent of contamination and identifying all affected distribution channels will likely remain challenging because of the complexity of fresh produce supply chains and reporting delays.

• Authorities are also investigating other outbreaks of cyclosporiasis nationally that are unrelated to the multistate outbreak. 

As of July 13, a total of 1,644 laboratory-confirmed Cyclospora infections associated with the multistate outbreak had been reported in Indiana, Kentucky, Michigan, Ohio, and West Virginia, with illness onset dates ranging from May 13-July 13. Epidemiologic investigations identified a common exposure among affected individuals, strongly suggesting contamination of a widely distributed food item.

On July 16, the FDA and CDC announced that traceback and epidemiologic investigations had identified shredded iceberg lettuce served at locations of a national fast-food restaurant chain in the five affected states as the likely source of the outbreak. Federal investigators traced the implicated lettuce to a single supplier and have initiated product testing, increased import screening, and are working with the supplier to determine whether potentially contaminated product remains on the market.

Health authorities are also investigating other outbreaks of cyclosporiasis nationally that are unrelated to this outbreak. Multiple states have reported substantially higher case numbers than during the same period in 2025. The largest outbreak is centered in Michigan, where authorities have reported 4,312 cases as of July 16, far exceeding the state's typical annual total of 40 to 50 cases. The Michigan outbreak provided much of the epidemiologic evidence that led investigators to identify shredded iceberg lettuce as the likely outbreak source. However, authorities continue investigating whether contamination extended beyond the currently identified distribution network.

Ohio has also experienced a substantial increase, with 1,119 cases reported as of July 15, primarily concentrated in the northwest of the state. Elevated activity has also been reported in Illinois, North Carolina, New York, Colorado, Indiana, Kentucky, Maryland, Florida, and several other states. 

Cyclosporiasis is a gastrointestinal disease caused by the microscopic parasite Cyclospora. It is transmitted through the consumption of food or water contaminated with the parasite. Unlike many foodborne pathogens, direct person-to-person transmission is considered highly unlikely because the parasite requires one to two weeks outside the human body before becoming infectious. Common symptoms include watery diarrhea, loss of appetite, weight loss, bloating, nausea, and fatigue.  

In the US, foodborne outbreaks of cyclosporiasis have historically been linked to imported fresh produce. Foods implicated in previous outbreaks include bagged salad mixes, fresh cilantro, fresh basil, raspberries, snow peas, and green onions. Cases typically increase during the spring and summer months, with US health authorities defining the cyclosporiasis season as May 1-Aug. 31.   

The increase in cases closely aligns with the annual US cyclosporiasis season, during which more than 90 percent of domestically acquired infections typically occur between May and August. Although seasonal increases are expected each year, the scale of the outbreaks in Michigan and Ohio is highly unusual. Federal investigations have now identified shredded iceberg lettuce as the likely outbreak source, supporting earlier evidence that a widely distributed fresh produce item was responsible.

Identifying the source of cyclosporiasis outbreaks is inherently difficult. The delay between exposure and symptom onset (2-14 days), combined with laboratory confirmation and reporting delays, means patients are often asked to recall foods consumed several weeks earlier. Although investigators have identified the likely contaminated food vehicle, determining the full scope of the outbreak remains challenging. Authorities are still assessing whether potentially contaminated lettuce remains in distribution and whether contamination affected additional restaurants, retailers, or supply chains. The long period between exposure and symptom onset, delayed diagnosis, and complex produce distribution networks continue to complicate outbreak investigations.  

Diagnostic limitations further contribute to underestimating the true disease burden. Cyclospora is not routinely included in all gastrointestinal testing panels, often requires specific clinical suspicion, and may require multiple stool specimens because the parasite is shed intermittently. Consequently, many infections are diagnosed weeks after exposure, while milder cases may never be tested or reported.    

Tracking cyclosporiasis outbreaks is also more challenging than investigating many other bacterial foodborne diseases. Unlike bacteria such as Salmonella, Escherichia coli, or Listeria, Cyclospora cannot be grown in routine laboratories, making it difficult to genetically link cases and identify a common source. Investigations are further complicated by delays in reporting from state health departments to the CDC. 

Additional cases are highly likely through August as seasonal transmission continues and delayed diagnoses are incorporated into surveillance data. While investigators have identified shredded iceberg lettuce as the likely source of the multistate outbreak, investigations remain ongoing to determine the full extent of contamination and whether additional distribution channels or exposure settings were involved. Continued traceback investigations and enhanced surveillance will likely identify additional outbreak-associated cases over the coming weeks, although public health interventions targeting the implicated supply chain should reduce the risk of ongoing exposure if contaminated product has been successfully removed from circulation. 

Cyclosporiasis is rarely life-threatening, and most cases recover with appropriate treatment. However, the exceptionally large scale of the outbreak, ongoing seasonal transmission, and the possibility that additional contaminated products or distribution channels may yet be identified continue to elevate the risk of foodborne exposure during the remainder of the seasonal transmission period.

Travelers and residents should follow standard food hygiene practices, including washing fresh produce thoroughly where appropriate, choosing cooked foods when possible, and seeking medical evaluation if persistent watery diarrhea develops. People can further reduce their risk of infection by:

• Washing hands with soap and water before and after handling fresh fruits and vegetables.    
• Washing all fruits and vegetables thoroughly under running water before eating, cutting, or cooking.    
• Scrubbing firm fruits and vegetables, such as melons and cucumbers, with a clean produce brush.    
• Cutting away damaged or bruised areas on fruits and vegetables before preparing produce.    
• Refrigerating cut, peeled, or cooked fruits and vegetables as soon as possible (within two hours).  

This represents the most complete data available as of July 17.  

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